A solar cell generates electricity using properties of a semiconductor, specifically, has a PN junction structure in which a P-type (positive) semiconductor and an N-type (negative) semiconductor are joined. When solar light is input to such a solar cell, holes and electrons are generated in the semiconductor by energy of the input solar light. In this case, by electric field on the PN junction, the holes are moved to the P-type semiconductor layer and the electrons are moved to the N-type semiconductor, thereby generating electric potential.
Solar cells may be classified into a substrate-type solar cell and a thin-film-type solar cell. The substrate-type solar cell is manufactured using a semiconductor material such as silicon as a substrate, and the thin-film-type solar cell is manufactured by forming a semiconductor layer in a thin-film form on a substrate such as glass. Recently, it is planned to improve efficiency through development of solar cells using the CIGS light absorption layer.
In order to raise photoelectric conversion efficiency of the solar cell, a ratio of the solar light absorbed to the light absorption layer has to be raised. In a case of the thin-film-type solar cell, it is possible to lower the manufacturing cost by using the light absorption layer of the thin film as compared with the substrate-type solar cell, but there is a problem that the light absorption rate is lowered. As a plan to overcome the decrease of the light absorption rate described above, it is necessary to increase the amount of solar light reaching the light absorption layer.
The thin-film-type solar cell generally has a structure of substrate/rear electrode/CIGS light absorption layer/buffer layer/front electrode. The solar light has to pass through the front electrode and the buffer layer to reach the light absorption layer. Accordingly, the front electrode and the buffer layer have to be made using materials with transmissivity of light, and the amount of solar light reaching the light absorption layer increases as the transmissivity of light gets higher, thereby further raising the photoelectric conversion efficiency.
(Patent Document 1) Korean Registered Patent Publication Registration No. 10-1108988 has an effect capable of realizing low reflection and high absorption of incident light by forming a front transparent electrode having a surface-crystalline uneven structure in the CIGS solar cell module. To this end, particularly, there is provided a CIGS solar cell module with a front transparent electrode having a surface-crystalline uneven structure, including: a rear electrode that is formed on a predetermined substrate; a CIGS light absorption layer that is formed on the rear electrode; a buffer layer that is formed on the CIGS light absorption layer; a front transparent electrode that is formed around the buffer layer and refracts predetermined incident light to transfer the incident light to the CIGS light absorption layer; and a reflection preventing film that is formed to prevent the incident light from being reflected on the front transparent electrode, wherein the front transparent electrode is formed of fluorine-contained tin oxide, and a surface-crystalline uneven structure for refraction is provided on the surface coming in contact with the reflection preventing film. The CIGS solar cell module is provided with the front transparent electrode having the surface-crystalline uneven structure, it is possible to thereby realize low reflection and high absorption of incident light, and there is an advantage that it is possible to adjust an unevenness angle capable of adjusting reflectivity in forming the surface-crystalline uneven structure of the front transparent electrode in the CIGS solar cell module. However, there is a disadvantage that the transparent electrode itself absorbs some of solar light.